Range of values (maximum - minimum) along an axis.
The name of the function comes from the acronym for ‘peak to peak’.
| Parameters : | a : array_like 
 axis : int, optional 
 out : array_like 
  | 
|---|---|
| Returns : | ptp : ndarray 
  | 
Examples
>>> x = np.arange(4).reshape((2,2))
>>> x
array([[0, 1],
       [2, 3]])
>>> np.ptp(x, axis=0)
array([2, 2])
>>> np.ptp(x, axis=1)
array([1, 1])